1. Field of the Invention
This invention relates to an apparatus for regulating the pneumatic pressure of a motor vehicle tire by charging a tire with air or discharging air from the tire.
2. Description of the Related Art
Well known systems for modifying the pneumatic pressure of a motor vehicle tire in response to the condition of the motor vehicle are disclosed in U.S. Pat. No. 4,782,878, 4,862,938 and 5,141,589.
With any of these disclosed systems, the pneumatic pressure of a tire is controlled to show a specified pressure level. If the actual pneumatic pressure of the tire is lower than the specified value, an inflation valve of the system is held open for a given period of time, whereas a deflation valve of the system is held open for a given period of time if the pneumatic pressure of the tire is higher than the specified value. The operation of opening the inflation valve or the deflation valve is repeated until the actual pneumatic pressure of the tire becomes equal to the specified pressure.
Since the inflation valve or the deflation valve is kept open for a predetermined period of time with any of the disclosed systems, the valves normally need to be driven to open or close frequently, spending considerable time, until the pneumatic pressure of the tire finally becomes equal to the specified pressure.